Definitely this, unfortunately. elementaryOS 0.4.1 Loki was fairly stable for me, but then I installed 5 / Juno, and now the machine often locks up with a completely black screen, except for a handful of items visible where the top menu bar usually is. It seems to occur when it wakes from a sleep mode (though this is on a Parallels virtual machine). The only solution is to reboot and lose whatever you were working on.
elementaryOS is great and the first Linux I've really enjoyed using (I'm normally a Mac user, the kind who uses software by Panic). But it still has so far to go. It's also worrying that you can't upgrade from 0.4.1 to 5. Even with all of Microsoft's disasters with updates, they've still managed to let you upgrade from one version of Windows to the next one.
(Did anyone else have these issues?)
You can break elementaryOS' nice graphics just by putting it into sleep mode and waking it up again - say hi to at least 2 different kinds of graphics glitches and possibly a randomly appearing bug in the file manager. And I'm not sure if it was a bug or a feature, but last time I used eOS I didn't enjoy the default video player's "fullscreen mode" in which it still didn't overlap the lower part of the desktop with the dock.
But keep in mind I haven't tried the most recent version which came out not long ago, I'd be surprised if some of the problems weren't fixed yet.
I think elementaryOS is on the right track, but it's definitely not more stable than the average distro, including the ones with rolling-release update models.